Differential parental investment is the sexual selection process in which females that have acquired an attractive male invest relatively more in his offspring than females that are paired to an unattractive male. However, it is often difficult to distinguish between differential parental investment and compensation for a decrease in parental investment by an attractive mate. Using Barn Swallows Hirundo rustica gutturalis, in which males rarely participate in incubation, we investigated differential incubation investment of females. We made the following four observations: (1) Females participate in 94% of total nest attentiveness (time that eggs were incubated). (2) Female nest attentiveness was positively correlated with the ornamentation of their mates, the size of white spots in the tail, which is a measure of male attractiveness in this population. (3) Male nest attentiveness was not related to male ornaments. (4) Total nest attentiveness was positively correlated with the size of white spots in the tail. These results are consistent with differential parental investment, but not with compensation for a decrease in parental investment by a mate. Therefore, we conclude that female Barn Swallows that have acquired an attractive male invest differentially in incubation.